202 DIGESTION. 



process, the anatomy of which will be considered farther on in treating of the temporo- 

 maxillary articulation. The anterior process, called the coronoid process, is for the at- 

 tachment of the temporal muscle, one of the most powerful of the muscles of mastication. 

 The greater portion of the external surface of the ramus, extending down to the angle, is 

 for the attachment of the masseter muscle. The internal surface of the ramus gives at- 

 tachment to several muscles ; viz., the external pterygoid, attached to the neck just be- 

 low the condyle, the temporal, the attachment to the coronoid process being much 

 more extensive on the internal than on the external surface, and the internal pterygoid, 

 which has its attachment at the angle. 



Temporo- Maxillary Articulation. The various classes of mammalia present great 

 differences in the temporo-maxillary articulation, differences which indicate, to a great 

 extent, their natural diet. In the carnivora, the long diameter of the condyle is trans- 

 verse, and it is so firmly embedded in the deep glenoid cavity of the temporal bone as 

 to admit of extended movements in but one direction. In these animals, lateral -and 

 antero-posterior sliding movements of the jaw are impossible, and there is very little 

 mastication of the food. In the rodentia, the long diameter of the condyle is antero- 

 posterior, the peculiar gnawing movements in these animals requiring a considerable 

 sliding movement of the lower jaw in this direction. In the herbivora, particularly the 

 ruminants, the condyle is small and slightly concave instead of convex as in most other 

 animals. It moves on a large projecting surface on the temporal bone, and the entire 

 jaw is capable of remarkably extensive lateral movements. 



In man, the articulation of the lower jaw with the temporal bone is such as to allow, 

 to a considerable extent, of an antero-posterior sliding movement and a lateral move- 

 ment, in addition to the ordinary movements of elevation and depression. The condy- 

 loid process is convex, with an ovoid surface, the general direction of its long diameter 

 being transverse and slightly oblique from without inward and from before backward. 

 This process is received into a cavity of corresponding shape in the temporal bone, called 

 the glenoid fossa, which is bounded, anteriorly, by a rounded eminence (erninentia articu- 

 laris), the uses of which will be more fully described in connection with the movements 

 of the jaw. 



Between the condyle of the lower jaw and the glenoid fossa, is an oblong, inter-ar- 

 ticular disk of fibro-cartilage. This disk is thicker at the edges than in the centre. It is 

 pliable and so situated that when the lower jaw is projected forward, making the lower 

 teeth project beyond the upper, it is applied to the convex surface of the eminentia ar- 

 ticularis and presents a concave surface for articulation with the condyle. One of the 

 uses of this cartilage is to constantly present a proper articulating surface upon the artic- 

 ular eminence and thus admit of the antero-posterior sliding movement of the lower jaw. 

 It is also important in the lateral movements of the jaw, in which one of the condyles 

 remains in the glenoid cavity and the other is projected, so that the bone undergoes a 

 slight rotation. 



Muscles of Mastication. To the lower jaw are attached certain muscles, by which it is 

 depressed, and others by which it is elevated, projected forward and drawn backward, 

 and moved from side to side. The following are the principal muscles concerned in the 

 production of these varied movements : 



Muscles of Mastication. 



Muscles which depress the lower jaw. 

 Mutcle. Attachments. 



Digastric Mastoid process of the temporal bone Lower 



border of the inferior maxilla near the sym- 

 physis, with its central tendon held to the side 

 of the body of the hyoid bone. 



